Expert Report

Induced Seismicity Potential in Energy Technologies (2012)

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In the past several years, some energy technologies that inject or extract fluid from the Earth, such as oil and gas development and geothermal energy development, have been found or suspected to cause seismic events, drawing heightened public attention. Although only a very small fraction of injection and extraction activities among the hundreds of thousands of energy development sites in the United States have induced seismicity at levels noticeable to the public, understanding the potential for inducing felt seismic events and for limiting their occurrence and impacts is desirable for state and federal agencies, industry, and the public at large. To better understand, limit, and respond to induced seismic events, work is needed to build robust prediction models, to assess potential hazards, and to help relevant agencies coordinate to address them.

Key Messages

Research has provided a better understanding of the factors that induce seismicity. Although existing faults and fractures are generally stable, changes in subsurface pore pressure, for example due to the injection or extraction of fluid from Earth's subsurface, may change the crustal stresses acting on a nearby fault and induce a seismic event. Net fluid balance appears to have the most direct correlation to the magnitude of induced seismic events, thus, energy technology projects that maintain a balance between the amount of fluid injected and the amount withdrawn may induce fewer felt seismic events than technologies that do not maintain balance.

Although the general mechanisms that create induced seismic events are well understood, scientists are currently unable to accurately predict the magnitude or occurrence of such events due to the lack of comprehensive data on the complex natural rock systems at particular energy development sites. Predictions of induced seismicity at specific energy development sites will continue to rely on both theoretical modeling, and data and observations from measurements made in the field.

Of all the energy-related injection and extraction activities conducted in the United States, only a very small fraction have induced seismicity at levels noticeable to the public (that is, above magnitude 2.0). Different energy technologies typically use different injection rates and pressures, fluid volumes, and injection duration—factors that affect the likelihood and magnitude of an induced earthquake.

Geothermal energy—the use of heat from the Earth as an energy source—usually attempts to maintain a balance between fluid volumes extracted for energy production and those replaced by injection, which reduces the potential for induced seismicity. However, site-specific characteristics can make a difference. For example, the high-pressure hydraulic fracturing undertaken to produce geothermal energy from hot, dry rocks has caused seismic events that are large enough to be felt.

Conventional oil and gas development extracts oil, gas, and water from pore spaces in rocks in subsurface reservoirs. Incidences of felt induced seismicity from conventional oil and gas development appear to be very rare.

Shale formations may contain oil, gas, and/or liquids. Shales have very low permeability that prevent these fluids from easily flowing into a well bore, and so wells may be drilled horizontally and hydraulically fractured to allow hydrocarbons to flow up the well bore. Hydraulic fracturing to date has been confirmed as the cause for small, felt seismic events at one location in the world. The process of hydraulic fracturing a well as presently implemented for shale gas recovery does not pose a high risk for inducing felt seismic events.

Tens of thousands of waste water disposal wells have been drilled in the United States to dispose of the water generated by geothermal and oil and gas production operations, including shale gas production. Water injection for disposal has been suspected or determined a likely cause for induced seismicity at approximately 8 sites in the past several decades. However, the long-term effects of increasing the number of waste water disposal wells on the potential for induced seismicity are unknown, and wells used only for waste water disposal usually do not undergo detailed geologic review prior to injection, in contrast to wells for enhanced oil recovery and secondary recovery.

Capturing carbon dioxide and developing means to store it underground could, if technically successful and economical, help reduce carbon dioxide emissions to the atmosphere. However, carbon capture and storage differs from other energy technologies because it involves the continuous injection of very large volumes of carbon dioxide under high pressure, and is intended for long term storage with no fluid withdrawal. The large net volumes of carbon dioxide that would help reduce global carbon dioxide emissions to the atmosphere may have potential for inducing larger felt seismic events due to increases in pore pressure over time; potential effects of large-scale carbon capture storage projects require further research.

Understanding hazard and risk related to induced seismicity is critical to any discussion of the option, but currently, there are no standard methods to implement risk assessments for induced seismicity. The types of information and data required to provide a robust risk assessment include net pore pressures and stresses; information on faults; data on background seismicity; and gross statistics of induced seismicity and fluid injection or extraction.

Four federal agencies—the U.S. Environmental Protection Agency, the Bureau of Land Management, and the U.S. Department of Agriculture Forest Service and the U.S. Geological Survey—and several different state agencies have regulatory oversight, research roles and responsibilities relating to different parts of the underground injection activities associated with energy technologies, but there are currently no mechanisms in place for the efficient coordination of governmental agency response to induced seismic events.